1. Field of the Invention
The present invention relates to a method for luminance compensation of liquid crystal display and its device, particularly to a method and a device for luminance compensation, which can adjust the input signal intensity to obtain better image quality and suit for the image adjustment of various liquid crystal displays or similar displays.
2. Description of the Prior Art
Because the liquid crystal display has advantages such as low in electrical consumption, light, small and high in quality etc., it gradually substitutes for the cathode ray tube (CRT) to be the principal product in display industry and suits for digital televisions, notebook computers or computer monitors. But the liquid crystal display has the problems of overlong response time and afterimage due to the liquid crystal molecular properties such as viscosity, dielectricity and elasticity etc. The luminance of the liquid crystal display is not so bright as that of the CRT.
If the input frame is the darker images such as night scene, then the luminance or the contrast of the display would be insufficient so that the viewer can't view the detail of the image. If the input frame is with high contrast, such as the picture photographed with the back to the light, then the gray levels of the brighter and the darker images are more so that the darker region in the frame is more darker, the brighter region in the frame is more brighter, and the two regions in the frame can't display the delicate gradations. There are buttons for luminance and contrast adjustment on the general displays. The viewer can adjust the luminance and the contrast of the image by hand to make images more clear and colors more plentiful, but the adjustment by hand is very troublesome for viewing dynamic images. Because the frame switch of dynamic images is quick and diversified, it is difficult for single luminance and contrast proportion to suit for various images. Therefore, it is needed to enhance the image contrast and make the gradations of the frame clear by the adjustment of the inner parts of the display.
Referring to FIG. 1, it shows a method of gamma adjustment for enhancing images in a prior art. The control device for gray level luminance is installed on the voltage driver of the liquid crystal display. When system judges that the luminance or the contrast of an image is insufficient, the original gamma curve will be risen to be the adjusted gamma curve, i.e. the gamma voltage is increased and the luminance of the display is enhanced, so the contrast and the luminance of the image are improved. However, the technology in the prior art has the following disadvantages:    1. A control device is required to control the voltage in the display, so the power consumption is high.    2. Each display has its characteristic, and the control device can't be adjusted for different panels due to its single function, so the ability to control the image is insufficient.
Therefore, the present invention provides a novel method for luminance compensation and its device to improve the disadvantages stated above.